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EXPERIMENTAL TESTS OF PILE-DRIVING, 



FOKMULA FOE RESISTANCE DEDUCED THEREFROM. 



COMPILED BY 



KICH'D DELAFIELD, Bv't Maj. Gen'l, 

Corps of Engineers, U. S. Army, Member of the L. H. Board. 



Washington, D. C, Dec. 1, 1868. 
PUBLISHED BY ORDER OF THE LIGHT-HOUSE BOARD. 



WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1868. 




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REFERENCES TO AUTHORITIES CITED IN THIS MEMOIR, 



1. Report to Engineer Department, by Captain Delafield, of the Corps of Engineers, July, 

1829, on the Geological Formation of the Outlets of the Mississippi Eiver. — (House 
Document, No. 7, First Session of Twenty-first Congress.) 

2. Comptes Rendus de PAcademie des Sciences. Triger's System for Foundations by 

Pneumatic Pressure. 

3. Crecy's Supplement to his Encyclopaedia of Civil Engineering. London, 1856. Iron 

Cylinders for Foundations sunk by Pneumatic Process. 

4. Hughes' Description of Foundations of Bridge at Rochester, England. Iron Cylinders 

sunk by Compressed Air. 

5. Memoir on Tubular Foundations. Le Pont de la Theiss, Vol. 17. Annales des Ponts et 

Chaussees for 1859. 

6. Pont sur Le Rhin a Kehl, par Vuigner et Fleur, Saint Denis, Paris, 1861. Pneumatic 

System of Foundations. 

7. Annales du Chimie, 1841. Pneumatic Process for Foundations. 

8. Rondelet, L'Art de Batir, Vol. 3. Weight of Massive Strictures on Foundations. 

9. Stewart's Dry Docks of the United States. Pile Foundations at Brooklyn, Philadelphia, 

and Pensacola,, and Experimental Tests on Pile-driving. 

10. Papers on Practical Engineering, No. 5, by Colonel J. L. Mason, U. S. Corps of Engi- 

neers, 1850, on Resistance of Piles to Pressure and Percussion at Fort Montgomery. 

11. Life and Services of Major John Sanders, of the Corps of Engineers, by Lieutenant 

St. Clair Morton, 1861, on Resistance of Piles at Fort Delaware and Experimental 
Tests on Pile-driving. 

12. General McAlester's Report to the Light-house Board on Resistance of Piles at Soutlv- 

west Pass, and at St. Joseph's Island." Bonzano's Letter of 9th of January, 1868. 

13. General McAlester's Report to the Light-house Board of the 5th of May, 1863. Modifica- 

tions of his Plans for Foundation of Light-house at Southwest Pass, and Views in 
Relation thereto. 

14. State Papers on Commerce and Agriculture. Commissioner's Report on Light-house at 

Mouth of the Mississippi River, built by Latrobe in 1817; also the Constructing Plans 
of the Building, loaned for reference, December, 1868, by Benj. H. Latrobe, Baltimore, 
Maryland. 

15. Records of the Light-house Board, Washington, D. C. Construction of Light-house at 

Southwest Pass in 1831, and at Pass a l'Outre in 1855. 

16. Henry Howard, Architect, New Orleans. Letters to General Delafield, June, 1868, on 

Foundation of a Church and Hotel in New Orleans, and other Structures in Louisiana. 

17. Annual Reports of the Chief Engineer, accompanying the President's Message to Congress, 

from 1824 to 1868. On Foundations and their Construction for the Forts in Louisiana, 
on the Rip-rap Shoal, Hampton Roads, and Fort Delaware, Delaware River. 

18. Records of the Treasury Department. Reports to the Architect from the Constructing 

Engineers on Foundations of Custom-house, New Orleans. 

19. Journal of the Franklin Institute for February and March, 186S. McAlpine's Iron 

Cylinder Foundation, Sunk by the Pneumatic System, modified by him, for the 
Bridge at Harlem, with Notes on Resistance of Iron and Wooden Piles. 

20. Report of the Light-house Board, accompanying the Report of the Secretary of the 

Treasury to Congress for December, 1868. Description of Pneumatic Process of 
Constructing Foundation for Waugoshance Light-house, Lake Michigan. 



21. Minutes of Proceedings of Institution of Civil Engineers, VoL 23. Description of the 

Wrought-iron Light-house at Ushruffee, Red Sea. 

22. Engineer and Architectural Journal for January, 1868. Description of Wrought-iron 

Light-house for the Douvres, between the Islands of Guernsey and Brehatr 

23. Proceedings of Institution of Mechanical Engineers for 1861. Description of Wrought- 

iron Light-house at Buda, Spain. 

24. Encyclopaedia Americana. Pile Foundations of the City of Amsterdam, 

25. Engineer and Scientific Journal for 1867. On Pile-driving. 

26,. Engineer and Architects Journal. On Foundations for Susquehanna Bridge, April, 1867, 
For the Clyde Viaduct, November, 1864. For the Albert Bridge, Saltash, Cornwall, 
1862 and 1864. On Bridge Pile Foundations, November, 1864. Opinions on London 
Bridge Foundations, January, 1858. For Foundations on Compressible Soils and 
Enlargement of the Base, 1857 ; and on the Grimsby Dock Foundations, 1864, 



Memoir on Foundations in Compressible Soils in connection with 
the adoption of a suitable artificial foundation for a light-house 
at the Southioest Pass of the Mississippi river. 

The following notes on the practice and experience of American and 
European engineers on foundations in very compressible soils are collected 
for the consideration of the committee of the Light-honse Board, to 
which was referred the different projects heretofore submitted for a 
foundation for a light-house to be constructed at the Southwest Pass of 
the Mississippi river: 

The soundings off the mouth of the river to the westward along the 
Louisiana and Texas coasts, and to the northward along the Chandeleur 
Islands, and thence eastward along the coasts of Mississippi and Ala- 
bama, all indicate sandy bottom beyond the immediate influence of the 
rivers. The advance of the delta of the Mississippi into the Gulf of 
Mexico is composed of alumina and vegetable matter overlaying this 
sandy bed. The depth of the sand below the waters of the river and 
gulf appears to be beyond our reach as a base on which to rest any 
artificial structure, and the surface of the soil created by the deposits of 
the freshets, is so deficient in solidity as to be designated very appropriately 
"prairie tremblante." "We have to combat the difficulties presented by 
this overlaying compressible mass. It is formed during the annual 
freshets of the rivers by deposits, in eddies and slack water, of the matter 
abraded by the current from the shores and banks of the different rivers 
as their freshets are thrown into the Mississippi, and not thrown up or 
translated along the coast by the ocean wave. These deposits from 
the tributaries of the Mississippi valley, vary in specific gravity, are 
deposited during the annual freshets in proportion to their gravity, and 
combined with more or less water in the porous mass form strata of 
varying density overlaying each other, and constitute the accumulation 
from year to year. 

A remarkable feature in this alluvial formation is the upheaval by 
some unaccountable power of islands that consist of the deep seated 
strata, raised and forced up many feet above the level of the gulf and 
annual freshets, leaving cavities beneath them, and an element of 
destruction in the continued discharge of matter mixed with water 
thrown up for an indefinite period after their first and sudden eruption 
and formation. They have been sufficiently described in previous reports 
to the Board, on its files, and now only referred to for indicating localities 



6 

the engineer should studiously avoid as beyond his power of adaptation 
for foundations of heavy structures, and, with the previous introductory 
remarks, to be considered with the projects of engineers for other difficult 
localities now to be noticed. (See House Document No. 7, 1st session 
of the 21st Congress.) 

HOLLOW IRON CYLINDERS SUNK BY ATMOSPHERIC PRESSURE. 

This system has been applied successfully in Europe and America. 
Having been proposed for the Southwest Pass light-house, the following 
notes are submitted explanatory of its advantages and applicability in 
certain localities: 

The first application of this principle is mentioned in Ure's Dictionary 
of Arts and Manufactures as having been tried on the Loire, in France, 
by Triger, in sinking a shaft 65 feet. A detailed account of Mr. Triger's 
system is to be found in the Comptes rendus de l'Academie des Sciences. 
The principle was applied by Mr. Hughes in sinking the piles at .Rochester 
bridge, England. With his modifications it has entirely superseded the 
ordinary diving-bell for foundations in deep water. Compressed air is 
made to free a hollow pile from the water within it after it has been 
.placed in its situation, (the bed of the river or other place,) there used as 
a diving-bell, without again being drawn up, and remains as a part of 
the permanent structure. 

Mr. Hughes sunk, on the Rochester side of this bridge, 12 cylinders or 
piles, and 30 on the Strood abutment ; each pile consisting of 2 or 3 or 
more sections of cylinders, 9 feet in length, 7 feet in diameter, bolted 
together through stout flanges, the bottom having a beveled edge. For 
a description of sinking these piles, see Crecy's Supplement to his Ency- 
clopaedia of Civil Engineering, London, 1856. Mr. Hughes' system is 
admirably shown on a large scale, with all its important details, in a 
work published by him in England. 

The agents of Dr. Potts, as a patentee, introduced it in this country, 
and it was successfully used by Mr. Gwynn for a railroad bridge in South 
Carolina, in a sandy bed of the Pee Dee river. Mr. McAlpine has used it 
with success for a bridge over the Harlem river, E". Y., in a muddy and 
sandy soil, and at this time it is being applied on a more enlarged scale 
under the Light-house Board, by General W. Sooy Smith, in the con- 
struction of a wall around the light-house at "Waugoshance, in Lake 
Michigan, in a gravelly and rocky bed. 

The Clyde or JSTethan viaduct is carried on cast-iron cylinders, sunk 
in the sandy bed of the river, filled up to the level of flood-tide with 
concrete, leaving upwards of 40 feet of the upper portion of the 



cylinders without any filling. (Engineer and Architectural Journal, 
November, 1864.) 

In the construction of the centre pier of the Albert bridge, at Saltash, 
on the Cornwall Railway, a wrought-iron cylinder, 37 'feet in diameter, and 
90 feet high, open at top and bottom, was sunk through the mud to the 
rock. It was expected that, forming a bank around the cylinder after 
being sunk to the rock, would exclude the water. 

The cylinder was constructed to admit also of air pressure; the 
surface of the rock was inclined 6 feet lower on one side than the other ; 
the iron cylinder was shaped to conform with the rock; a dome or lower 
deck was constructed inside at the level of the mud, 13 feet below the 
surface of the water; and an internal cylinder, open at top and bottom, 
connected the lower with the upper deck of the cylinder; a 6-foot 
cylinder was fixed eccentrically inside the other, and an air-jacket or 
gallery, making an inner skin around the bottom edge below the dome, 
was formed about 4 feet wide, divided in 11 compartments, and connected 
with the bottom of the 6-foot cylinder by an air passage below the 
dome. 

When the 37-foot cylinder was thus constructed, it was towed to and 
accurately adjusted over the intended site ; water was then let in, until 
the cylinder penetrated through 13 feet of mud, and rested on some 
irregularity, causing it to keel over about 7' 6 // . By letting water in 
upon the dome or lower deck, and loading the higher side with iron 
ballast, the cylinder forced its way through the obstruction at the bottom 
edge, and took a nearly vertical position. 

The air and water pumps were then worked, and the greater part of 
the mud and oyster shells which filled the compartments of the air- 
jacket was cleared out, and the irregular surface of the rock excavated — 
the bottom of the cylinder being now 82 feet below high- water line. A 
ring of ashlar stone, 4 feet wide and 7 feet high, was then built in the 
air-jacket, and a bank of clay and sand was deposited around the outside 
of the cylinder to compress the mud. 

When the water was pumped out the body of the cylinder below the 
dome, and the excavation of the mud was being proceeded with, a leak 
broke out and the water overpowered the pumps. Recourse to air 
pressure in the body of the cylinder below the dome was determined 
upon and arrangements made therefor. 

The 37-foot cylinder was loaded with 750 tons of ballast when the 
pumps succeeded in keeping the water down; the mud was then exca- 
vated, the cylinder below the dome securely shored across, and the rock 
leveled, when the masonry was commenced in the body of the cylinder. 

As soon as the masonry reached the level of the air-jacket ring the 



8 

plates of the air jacket were cut out, and the two masses of masonry 
were bonded and thus united, forming a single mass. Upon the top of 
the bonding course of masonry two courses of brick were laid in cement, 
making a water-tight floor over the whole diameter of the column. 

The next operation was to draw off the water above the dome and 
remove the ballast, allowing the masonry within to proceed. After the 
masonry had been completed to the plinth course the upper part of the 
cylinder was unbolted at the separate joints and floated to the shore. 

The roadway is 100 feet above high-water mark. This centre pier 
supports iron arches of 455' span each from the centre of the river. 
(Engineer and Architectural Journal, 1862 and 1864. 

Bridge over the Harlem river, on cast-iron cylindrical piles, by ¥m. J. 
Mc Alpine. The draw pier of this bridge was composed of one central 
and ten circumscribing iron columns, each 6 feet in diameter and 50 
feet in height h — the water being 20 feet in the deepest part. These 
piles were sunk by the pneumatic process, (both plenum and vacuum.) 
It was deemed advisable to increase even the large base, due to the size 
of the column formed by these cylinders. 

It had been decided to fill the columns with concrete; and it was 
suggested to extend this masonry below the bottom of the iron cylinders, 
(as the men could work in water,) undermining the adjacent earth as far 
as practicable, and to extend the concrete into the space thus undermined. 
This was done in sections of about 2 feet in width; and, when the rim 
had been completed, it was found that the column was virtually extended, 
and that the water would readily sink, under the pneumatic pressure, to a 
level with the bottom of the concrete, so that the sand within it was 
easily removed, and the space filled with concrete to a depth, generally, 
of 4 feet or more. The cement set with greater rapidity under pneu- 
matic pressure than in the open air. 

The last column was driven from 16 to 20 feet, in from 3 to 6 days, 
in sand and porous material, free from obstruction; 12 men, all told, 
sufficed to do the work, including engine-drivers, stevedores, and foremen. 
The metal in the columns was 1£ inch thick. No ill effects were expe- 
rienced by the workmen from a pressure of 2 J atmospheres. 

In some cases the pile could be sunk by the vacuum process alone; 
in all other cases by the plenum, and sometimes both might be employed 
with advantage, and further aided by weight or pressure on the heads of 
the cylinders. 

The support of these iron columns, derived from friction on the exterior 
surface, was found to be j- a ton per square foot, but in the finest earth 
it would amount to 3 tons. 

The support from the area of the bottom in shallow depths was from 



5 to 10 tons per square foot. (See Engineer and Architectural Journal 
for January, 1868.) 

This system is perfectly reliable in all cases where the compressible 
soil can be removed and a hard bottom reached on which to found the 
contemplated structure. It was practiced with great success in the con- 
struction of the Theiss bridge, and minutely described in the Annales des 
Ponts et Chaussees, 1859, and Annales du Chimie, (1841.) Mr. McAlpine 
gives much useful and practical information on this subject in the Feb- 
ruary and March numbers of the Journal of the Franklin Institute. For 
a foundation at Waugoshance, Lake Michigan, on this system for a wall 
of 8 feet thick, and laid 12' 3" below the surface of the water, 7 feet of 
which was through gravel and large boulders, enclosing an elliptical area 
of 67' by 49', under one wrought-iron cylinder, with air-pumps and 
valves, see the Report of the Light-house Board, accompanying the 
Report of the Secretary of the Treasury for December, 1868, pp. 71 
and 72. 

PILE FOUNDATIONS. 

The next system for consideration is that of piles driven into the 
ground, on which the superstructure rests directly, or through the inter- 
vention of a floor of wood or masonry. It is deserving of particular 
attention from its probable fitness for the locality under consideration at 
the Southwest Pass of the Mississippi river. 

FOUNDATIONS ON WOODEN PILES.— AMSTERDAM. 

The most extensive and oldest application of pile-driving for foundations 
to which instructive reference is at command is in the city of Amsterdam. 
The original site of this city was a salt marsh. All the buildings, (28,000,) 
for a population of 224,000 souls, (in 1850,) covering a surface of 900 
acres, are supported on piles of from 50 to 60 feet in length. After 
passing through a mixture of peat and sand of little consistence, at a 
depth of about 40 feet, they enter a bed of firm clay. The ends of the 
piles are sawed level, and covered with thick plank, on which the masonry 
is constructed. Though the houses have declined from the perpen- 
dicular, they are considered to be quite secure against falling; yet such 
a contingency occurred in 1822, by the sinking and total ruin of a large 
stack of warehouses heavily filled with corn — (wheat in bulk that shifted 
the weight.) 

The palace built in 1648 is supported on 13,659 piles. It is 282 feet 
long, 235 feet wide, and 116 feet in height, exclusive of a cupola of 
41 feet. 

The steeple of the Oude Kirk is 240 feet high. The surface or level 
of the natural ground is below the level of the ocean. 



10 

FOUNDATIONS ON WOODEN PILES AND CAISSONS IN THE BED OF THE 

THAMES, LONDON. 

The labors of engineers in the valley of the Thames river, at and 
about London, give much useful information in the construction of 
ancient as well as modern pile foundations. 

Old London bridge was commenced in 1176, and finished about 83 
years thereafter. The piers rested on piles driven only around the out- 
side of the pier, so placed as to carry the whole weight. They were of 
elm, and at the expiration of six hundred years, on being drawn up, 
remained without material decay. A part of this bridge fell about 100 
years after it was finished ; and the whole structure was removed to give 
place to the new bridge in 1825. 

Old Westminster bridge was built between 1733 and 1747. Piles 
were used under one pier only. Its piers (with the one exception) were 
constructed in caissons or flat-bottomed boats. Each caisson contained 
as much timber as a forty-gun frigate. They were 80 feet long by 30 
feet wide. These foundations failed; the caisson bottoms or floors sunk in 
the middle ; the sides and ends projecting beyond the stone work broke 
off and bent upwards. The sinking of the bearing area of the sub- 
stratum, under the partial and unequal pressures of the floors of the 
caissons, has had more to do with the failure than any other defect. 

Black Friars bridge was built between 1760 and 1771. The founda- 
tions were laid in caissons, the floors of which rested on piles about 9 
feet apart — only 45 piles to each caisson — and intended to obtain a level 
surface on which to rest the floor, to settle down to a uniform bearing. 
Its stability, says Rennie, for many years is to be attributed to these 
piles. It has since failed, and requires large expenditures on repairs. 

It was believed in this case, as at Westminster, that if the scour of 
the river bed could be prevented, and nothing carried away from under 
the foundations and about the piles by external agency, the clay base 
would support the gravel stratum above it, and the gravel the stone; 
but the pressure per foot in the Westminster was nearly 5 \ tons, and in 
Black Friar's 5 tons per square foot; and clay, when the pressure is at 
great depths within it, will not bear 5 tons per foot. 

Waterloo bridge, built between 1809 and 1817. The foundations of 
the piers of this bridge are built in coffer dams or caissons, the floors of 
which rest on piles, about 3 feet apart, under the entire base of the pier, 
penetrating the clay about 18 feet. The foundation is arranged with 
plank, concrete, and stone, as in the New London bridge. The estimated 
pressure per foot on the head of each pile is, in this case, about 68 tons. 
The arches are 120 feet span, and weigh about 2,500 tons each. 



11 

Vauxhall bridge was built between 1811 and 1816. The foundations 
of the piers of this bridge were built in caissons. An excavation was 
made down through the gravel stratum to the clay. It is a light struc- 
ture, and no settlement is recorded. 

New London bridge, built between 1825 and 1831. The foundations 
of the piers of this bridge are built in coffer dams or caissons, the floors 
of which rest on piles under the entire area of the bases of the piers. 
The piles are about 20 feet long and 3 feet apart, penetrating the clay 
18 to 19 feet. On the heads of the piles were laid sleepers; the loose 
earth between the heads of the piles is replaced with rubble concrete, 
on which blocks of stone and brick work filled up the spaces between 
the pile heads and immediately over the platform of oak .planking winch 
carried the first course of granite. 

The pressure upon each pile is 80 tons, or 5 tons per square foot of 
the entire area of the pier. Each pier of this bridge settled from six 
to ten inches towards the down stream. No further settling is appre- 
hended. 

Hungerford bridge, built in 1844. This is a chain suspension bridge. 
On the Hungerford market side the ground under the mooring piers was 
very bad. Piles were here driven to the depth of 30 feet. 

Chelsea bridge, built between 1850 and 1857. This is a suspension 
bridge. The foundations of the piers are on bearing piles of 14 inches 
square, 3' 6" apart, and driven 32 feet below low water, and about 16 feet 
into the London clay. For other details of these foundations see 
Engineer Architectural Journal, for November, 1864. 

New Westminster bridge, built in 1858 and since. The arches of this 
bridge are of wrought and cast iron. Elm piles, 32 feet long, are driven 
in alteruate rows of 3 and 5 each, to the number of 145 in each pier, 
and 18 to 20 feet into the London clay, each tested to a bearing weight 
of 60 tons. Circumscribing the area into which the elm piles are driven, 
hollow cast-iron piles, 15 inches diameter, 25 feet long, are driven 4 feet 
apart, and between these, in grooves cast on hollow piles, flat iron piles 
are driven to nearly the same depth, forming a coffer dam, within which 
all the soil overlaying the gravel bed is excavated, and concrete filled in 
to the top of the piles, which are cut off 6 inches below low water. 

On the heads of the elm piles is a course of stone covering two or 
three piles alternately, upon this the bottom course of granite of large 
size is laid. The bearing piles are 14 inches square, driven at intervals 
of V 9" from centre to centre, to an average depth of 20 feet in the 
London clay. It will thus be noticed that the solid stone piers sustaining 
the iron arches, rest upon the heads of the wooden piles, which stand 
a considerable height above the bed of the river; that these piles are 



12 

within an enclosure of cast iron and granite slabs; and around the piles 
and filling up the sides of the casing or enclosure there is a solid bed of 
concrete as good as rock. 

At the Hull docks the load per pile per square foot is 37 tons; at the 
London bridge the load per pile per square foot is 80 tons; at the Albert 
warehouse, Liverpool, the load per pile per square foot is 80 tons ; and 
at the New Westminster bridge it is 12 tons per square foot. And the 
pressure on the whole area of the foundation is only 2 tons, while on the 
old bridge it was 6 tons, and in the London bridge it is 5£ tons. 

REMARKS OF ENGLISH ENGINEERS ON THE LONDON BRIDGES. 

The bed of the Thames is much lower than when the bridges which 
have failed were built, occasioned by the increased scour produced by 
removing the old London bridge. Whenever the foundations have been 
made to depend on the gravel, and have not been taken deep into the 
London clay, failure has taken place. In the clay only can a foundation 
be found. 

The old successful examples are all of one class — coffer dam examples, 
(excepting Yauxhall and Mr. Page's recent structures.) Yauxhall was a 
coffer dam carried to the clay without piling; the weight of the bridge 
not needing piles. 

All the other sound bridges are piled deep into the blue clay. The 
shoulders and sides of these piles, and the surface of the clay between 
them at their tops, are the ultimate bearing points, upon which presses 
the superstucture, whether of granite or other stone courses, or composed 
of concrete and wood, or of iron. 

The concrete and iron casing about the piers of the Westminster, is 
believed to be a ten times stronger medium, for the retention of the piles 
in their places, than the London clay (at whatever depth) would be; and 
omiting, therefore, all aid from the external piles and casing in bearing 
the weight, we find that the 133 elm-bearing piles are alone capable of 
bearing a load four times greater than can be put upon them, and 
there is not so much chance for unequal settling as with sleepers and 
bearing planks, such as exist at the successful bridges. We cannot find 
one instance of deep piled bridges abroad which has fallen. 

In Venice the piles are covered with a planking of fiat boards under 
water. Whilst the London clay would only bear a pressure of 5 tons 
per foot, piles driven into it would carry 70 to 80 tons. 

At the Hull docks the piles were 10 inches in diameter, and carried a 
weight of 37 tons per foot superficial; at the London bridge the piles 
were 10 inches in diameter, and carried a weight of 80 tons per foot; at 
the Albert docks, Liverpool, the piles sustained a weight of 80 tons per 



13 

foot ; at the New Westminster bridge the piles were 14 inches in diameter, 
and would have to carry only 12 tons per foot. It was stated that the 
elm piles used in the foundations of Westminster bridge would carry 200 
tons without permanent deflection. (See Engineer and Architectural 
Journal, for 1858.) 

The compressibility of oolitic and tertiary clays can only be overcome 
by piling, deep sinking, heavy ramming, or heavy weighting. The 
point of bearing must be carried below the possibility of upward reaction. 
The depth of a foundation in compressible ground ought not to be less 
than \ the intended height of the building above ground — that is, for a 
shaft of 200 feet the foundations should be made secure to a depth of 50 
feet, by piling or by well sinking and concrete. (Engineer and Archi- 
tectural Journal, for 1857.) Masses of concrete, brick or stone, placed 
on a compressible substratum, however cramped and bound, may prove 
unsafe. Solidity from a considerable depth can alone be relied upon. 
Mere enlargement of a base may not in itself be sufficient. (Engineer 
and Architectural Journal, for 1857.) 

FOUNDATIONS OF THE GRIMSBY DOCKS ON THE HUMBER. 

These docks were commenced in 1846. The entrance to them is 
beyond the low- water line, and advanced into the river f of a mile. 
The ground over the whole area of the two entrance locks, centre pier, 
and wing walls was excavated 8 feet below the sill of the larger lock, and 
bearing piles were driven in rows 5 feet from centres, and in some places 
4 feet over the whole area. A pile was considered sufficiently driven 
when it moved not more than \ of an inch with the blow of a ram of 
1 ton falling 12 feet." The heads of the piles were then cut off to a 
uniform level, the ground was removed to a depth of 2 feet below this 
level, and the space filled with concrete. Timbers so connected as to 
form continuous ties across the locks and centre pier were then laid 
transversely in parellel rows on the bearing piles. Other similar timbers 
were laid at right angles to the tranverse bearers, concrete being filled in 
to the upper surface of these longitudinal bearers, which were then covered 
with planking as a bed for the masonry. (Engineer and Architectural 
Journal, for 1864.) 

The result of European experience gives the following as the bearing 
weights supported by the foundations of the piers of several of the most 
remarkable and heaviest structures, in pounds per square foot : 

Dome of St. Peter's, Rome 35,254ft>s. 

Dome of St. Paul's, London 41,7139*. 

Dome of the Invalid, Paris 31,862fts- 



14 

Dome of the Pantheon, Paris 43,440ft>s. 

Column of the Basilica of St. Paul 42,950ft>s. 

Steeple of the Church of St. Mary 63,325ft>s. 

For the relation between the total surface covered and the part 
occupied by its walls, or the supporting parts and the above, see Pondelet, 
Vol. 3, p. 232. 

PEACTICE AND EXPERIENCE OF UNITED STATES ENGINEERS. 

We now proceed to give the practice and experience of the Engineers 
of the United States, in the construction of foundations in different 
localities and in compressible soils. The dry dock at the Brooklyn .Navy 
Yard, New York, was commenced in 1841 and completed in 1851. It 
contains 13,837 cubic yards of masonry, resting upon 38,532 cubic feet 
of pile timber. 

The soil was found to be chiefly vegetable decompositon to the depth 
of 10 feet, and below this almost impalpable quicksand containing a large 
proportion of mica. When confined, and not mixed with water, it is very 
firm and unyielding, presenting a strong resistance to penetration. 
When saturated with water it becomes a semi-fluid, and moved by 
the slightest current of water passing over or through it. Small veins 
of coarse sand were also occasionally encountered, through which flowed 
springs of fresh water. Borings were made to the depth of 80 feet, and 
brought up sand and clay and fresh water. There is but a small propor- 
tion of clay in any part of the foundation. The borings extended 40 
feet below the foundation of the dock. 

The foundations for the superstructure of this dry dock were placed 
37 feet below mean tide and 42 feet below the surface of the ground. 
Black mica overlaid the quicksand under the coffer dam. Under and 
in this coffer dam 3,504 piles were driven, averaging 39 feet in length by 
15 inches square. ■ 

The earth above low water was removed before the coffer dam was 
formed, and about 10 feet in depth was removed by dredging. The semi- 
fluid state in which the material was found after the water had been 
pumped out of the pit, was very difficult to remove. It was so fluid as 
to require tubs for its removal. Bottom springs of fresh water were 
found in about six feet of the required depth of the foundations. The 
largest discharged 10 gallons per minute. When flowing from a level of 

26 feet below low water it discharged 38 gallons per minute, containing 

27 ounces of sand; at a level of 22 feet, it discharged 33 gallons per 
minute, containing 17 ounces of sand; at a level of 17 feet, it discharged 
10 gallons per minute, unmixed with sand. 



15 

These springs presented great difficulties in laying the foundations from 
the flowing of the water, which as it came np brought large quantities of 
sand, which, if continued to flow, w^ould soon have endangered the sur- 
rounding works. The pressure of the water was so great as to raise the 
foundation however heavily it could be loaded. 

The settling of the piles supporting the pump well, was the first 
evidence of undermining from one of these springs. The site of the well 
was changed but the spring followed, and compelled another change of 
the well. 

This spring was driven out of the old well by driving piles until it was 
filled up, but it immediately burst up among the foundation piles of the 
dock near by. In a single day it made a cavity in which a pole was run 
down 20 feet below the foundation timbers. 150 cubic feet of stone 
were thrown into this hole, which settled 10 feet during the night, and 
50 cubic feet more were thrown in the following day, which drove the 
spring to another place where it undermined and burst up through a bed 
of concrete 2 feet thick. This new cavity was repeatedly filled with 
concrete, leaving a tube for the water to flow through ; but in a few days 
it burst up through a heavy body of concrete in a place 14 feet distant, 
where it soon undermined the concrete, and even the foundation piles, 
which settled from 1 to 8 inches although 33 feet long, and driven by a 
hammer of 2,200ft»s falling 35 feet at the last blow, with an average of 76 
blows to each pile, the last blow not moving the pile -J an inch. It was 
then determined to drive as many additional piles into the space by means 
of followers to force those already driven as deep as possible. 

The old concrete was then removed to a depth of 20 inches below the 
top of the piles. An area of about 1,000 square feet around the spring was 
then planked, on w T hich a floor of brick was laid in dry cement, and on 
that another layer of brick set in mortar. The space was next filled with 
concrete, and the foundations completed over all. Several vent holes 
were left through the floor and foundations. After a few days when the 
cement had well set, the spring was forced up to a level of about 10 feet 
above the former outlet, at which it flowed clear without sand. 

Two other of these springs were closed by freezing in 1848 and forced 
up in one case 800, and in the other 1,200 square feet of the foundations. 
This took place between the lower timbers and the planking, lifting also 
the first course of the stone floor, which was from 12 to 15 inches thick. 

The w T hole number of bearing piles in the foundation is 6549. They 
are chiefly round spruce timber 25 to 40 feet long, averaging 14 inches 
diameter at the head. The average length of all the piles driven was 
32' 7". The piles were originally driven 3 feet from centres. After- 
wards as many piles were driven as could be forced into the earth. 



16 



"Whenever a hammer of 2,000ft>s weight, falling 35 feet, drove the pile for 
the last few blows, exceeding 3 inches per blow, another and larger pile 
was driven along side. 

With the exception of 541, all these piles were driven by hammers 
from 2,000 to 4,500ft>s each, falling from 35 to 40 feet. The average 
number of blows per pile was 151 with the small hammers, and 50 
blows only per pile with the large hammers. The 541 piles were driven 
with a [Nasmyth steam-pile engine. 

A trial round pile of (20") twenty inches diameter at the butt, and 
(14") fourteen inches at the small end, of 49 feet in length, was driven 
by a 20241b hammer, falling finally 35 feet; forty-five feet below the 
foundations. The first 100 blows the hammer fell but a few inches; the 
next 260 blows drove the pile 30" in 46 minutes; the next 260 blows 
drove £" to 1J" per blow for 60 minutes; the next 110 blows averaged 
1£" per blow for 60 minutes, the hammer falling the last blow 34 feet. 

This trial pile subsequently received 200 blows through the medium of 
a follower which drove it an average of £ an inch to each blow. 

Another trial pile was driven 43 feet by a Nasmyth steam-pile driver, 
and then another pile 15 feet long, driven on top of the first, making a 
total penetration in the earth of 57 feet. 

The first pile was driven 42 feet by 373 blows in 7 minutes as follows: 

4 blows, 4 inches each. 



8 


" H 


22 


" 3 


25 


< 2 


40 


' n 


56 


1 n 


32 


' H 


64 


u i* 


73 


' i 


49 


< i 



The second pile was driven 15 feet by 2,400 blows in 43 minutes as 
follows : 

33 blows, f of an inch each blow. 



73 < 


' i 


u 


a 


a 






100 < 


1 i 


a 


a 


a 






800 < 


' drove it altogether 88 inches 


t 


300 < 




a 


a 


24 


u 




300 < 




a 


a 


12 


a 




450 < 




u 


a 


11 


a 


and the last 


350 < 




a 


a 


n 


a 





17 

The movement of these piles indicated the continuance of the same 
material to the depth which they reached. 

The foundation was mostly laid as follows: The excavation being 
completed to the proper depth, and piles cut off to a uniform level, 2 
feet in thickness of concrete was rammed between the bearing piles. 
These piles were then capped with 12 and 14 inch yellow pine timber, 
laid transversely with the axis of the dock, and tre-nailed to each pile. 
The concrete was then raised to the top of these timbers, and a light 
flooring of three inch yellow pine plank was laid upon and spiked thereon. 
Another course of similar timber was then placed upon this floor, break- 
ing joints with those below, to which they were tre-nailed. The intervals 
were next filled with concrete, and another floor of 3-inch plank spiked 
down; which completed the foundation. 

The amount of work done by the heavy Nasmyth hammers was at least 
J greater than that done by those whose hammers were only ^ the weight. 
This Nasmy th hammer of 4,500ft>s was worked with very short rapid blows, 
raised a height equal only to the stroke of the engine* 

The support of this foundation is derived mainly from the adhesion of 
the material into which the piles were driven and slightly from their 
sectional area. 

It was ascertained that it required a weight of 125 tons to draw up one 
of these piles, or rather to start or put it in motion, when driven 33 feet 
to the point of ultimate resistance, with a ram of one ton falling 30 feet 
at the last blow. The piles averaged 12" in diameter in the middle, 
making at least a support of 100 tons per square foot of foundation. 

PILE FOUNDATIONS AT THE PHILADELPHIA NAVY YARD. 

At the site of the dock of the Philadelphia navy yard, commenced in 
1849, the first stratum of soil is a mud of rich loam extending from a 
little above low water level, declining towards the bottom of the river, 
which is of a clean gravel, to the depth of about 24 feet below ordinary 
low tide, and evidently the deposit through a long period of years of the 
earthy matter held in suspension by the waters of the Delaware .River, 
upon a stratum of sand and gravel forming the bed of the river. The 
sand and gravel are not more than from 4 to 7 feet in thickness, before 
those substances become mingled with paving stones, large boulders, and 
to some extent with clay, forming a species of hard pan, to which all the 
piles used in the construction of the foundations of the work were driven. 
The object of the foundation of the basin of the dock, was to give support 
to its bottom, and to secure its outer edge against the action of the current 
of the river. As the excavation was completed, piles were driven 4 feet 

Memoir, etc. 2 



18 

apart from centres in rows from one end of the space to the other. An 
extra row was driven under the line of the walls of the three sides of the 
basin. A space was then formed by drawing a line of sheet piling eight 
feet from the inner line of piles of the coffer dam. Two extra rows of 
piles were driven within this space, which was then filled with concrete 
to within 2 feet of the floor of the basin. The piles thus driven were 
cut off to the same level, capped with timbers one foot square, and the 
spaces between these capping timbers filled with earth and concrete. 
(Stewart's dry docks of the U. S.) 

PILE FOUNDATIONS AT THE PENSACOLA NAVY YARD. 

The dock at the Pensacola navy yard was built in 1851 and 1852. 
The soil of this locality is clean white sand, to a depth of about 40 feet, 
resting upon a bed of soft clay. The sand is so open and porous that a 
cubic foot of it, when saturated, contains 6 quarts of water. 

A space of 140 feet wide by 380 feet long was enclosed by driving 
yellow pine piles, 12 inches square, to the depth of about 20 feet into 
the sand, placed in contact with each other, for forming a coffer dam. 
Within this space, secured by other means against filtration, the sand 
was excavated to a depth of 14 feet below tide. 

After a section of the pit had been excavated to the level of the 
foundations, the bearing piles were driven in rows 4 feet apart, and 4 
feet from centres in each row, until a ram of 2,200 pounds, falling 30 feet, 
could not move them more than ^ an inch. Upon the transverse rows 
of piles, cap timbers, 12 inches square, were placed, and the space between 
the timbers filled with sand. The timbers were then covered with 5-inch 
plank, spiked to the caps, and the whole floor caulked with wedges. On 
this floor the masonry of the basin was commenced. This foundation 
was tested and found satisfactory. The experimental tests showed that 
a single foundation pile, as a fulcrum, sustained nearly 39 tons without 
settlement; and it required 41 tons strain to draw a pile that had been 
driven 16 feet into the sand. 

The railroad bridge at Havre-de-Grace, on the Susquehanna river, was 
commenced in October, 1862, and finished in November, 1866. 

The foundations of the piers of this bridge are referred to as examples 
of piles driven in the compressible bed of the river, supporting an iron 
caisson on a grillage of timber resting on the piles, and a caisson lowered 
to solid rock through 15 feet of compressible soil. 

In 1863 piles were driven and sawed off 40 feet below the surface of 
the water for the foundation of pier No. 3 ; a platform or grillage of 
timber, strongly ironed, upon which the pier was to rest, was constructed 



19 

near the site of the work and floated over the site of the foundation 
under which the piles had been driven. This platform was placed 
between two substantial construction piers of timber; lowering screws, 
6 in number, of 3£ inches diameter, were attached by hooks to the plat- 
form; and to the construction piers a section of an iron caisson was 
constructed, resting upon the wooden platform thus suspended. The 
masonry was then built within the caisson, lowered by means of the 
screws, as it approached the top of the section, when a second section of 
the iron caisson was added, built within and lowered by the screws in 
like manner as the preceding, and thus continued until the grillage or 
wooden platform rested upon the heads of the piles. 

Another pier (No. 7) was founded on the rocky bed of the river 
underlaying the compressible bed of the stream for a depth of 15 feet. 
This latter had been displaced in several places by the spring freshets of 
1865, rendering piling impracticable; all the earth was, in consequence, 
removed down to the surface of the rock. At the site of this pier the 
rock bed was 18 feet below the original undisturbed bed of the river. 
To remove this earth a wrought-iron foundation caisson, averaging 8 feet 
in height and about 50' by 20' square, was lowered so as to enclose the 
site of the pier. This was gradually depressed to the rock by removing 
the earth within it by means mainly of powerful pumps, aided by the 
constant exertions of skilled divers. The masonry was then laid within 
the tank upon the solid rock, and being brought to a level some feet 
below the top of the foundation caisson; the caisson of the pier resting 
upon the platform of timber was lowered and built upon. The founda- 
tion of this pier was 36 feet below low water. (See Engineer and 
Architectural Journal, April, 1867.) 

RESISTANCE OF PILES TO PRESSURE.— FORT RICHMOND, STATEN ISLAND, 

NEW YORK. 

The soil of part of the foundations of Fort Richmond, now Fort 
Wadsworth, on being excavated to low-water level, was found to be very 
compressible, with springs discharging large quantities of water. The 
scarps and counterscarp of the southern half of the land front and face 
of the adjacent bastion of the water front were situated on such a soil, 
resembling that of the dry-dock at Brooklyn. The weight to be sustained 
was a granite casemated battery of four tiers of 8 and 10-inch guns, 
with the shot, shell, and other munitions therefor. The scarps, piers, 
and arches, are all of granite. 

Piles were in this case resorted to, and no settlement has since been 
noticed. The work was commenced in 1856, and finished to receive 
its armament in 1861. The piles were 30 feet long, 12 inches square at 



20 

the head, and not less than 10" at the small end. They were driven by 
a hammer of 1,800 pounds weight, with blows in quick succession, the 
last blow of the hammer being from a height of 45 feet. They were 
cut off level with the surface of the ground, and capped with large flat 
stone, covering the heads of from 3 to 5 piles — the joints being filled 
with concrete, well rammed. A second layer of large flat stone, break- 
ing joint with the first, on which the masonry of the granite scarp was 
commenced. It will be noticed that there was no timber grillage 
covering the heads of these piles. 

EESISTANCE OF PILES TO PRESSURE.— EXPERIMENTAL TESTS AT 

PENSACOLA. 

In 1851 a series of experiments were made, under the direction of a 
special board of officers, on the resistance, etc., of the piles driven for the 
foundations of the dock of the navy yard at Pensacola. A pile that had 
been driven six days, surrounded by other piles 4 feet distant from cen- 
tres, of 30 feet in length, averaging 13 inches diameter about the middle 
of its length, round, with bark on, was first selected for these experiments. 
The average depth of the pile in compact sand was 15 feet, driven by 
a hammer of 4,087 pounds and 69 blows, at the rate of 2 J blows per 
minute. 

The first experiment, made on the 17th of May, was the application 
of a power (by pressure or loading) of 23,850 pounds to a pile for 5 
minutes, which it bore without moving. The second experiment was by 
applying a power of 20,000 pounds to another pile ; a third pile was 
subjected to the same strain for 5 minutes, and a fourth pile resisted the 
same power for 5 minutes. There was then applied to this last pile 
31,360 pounds (14 tons) for several minutes. Three other piles were 
subsequently tried, and each resisted 22,400 pounds (10 tons) pressure for 
5 minutes. 

The next test was by pulling up the piles, beginning with 22,400 
pounds, applied to the pile No. 4, before noted, increasing the power 
one ton every two minutes — that is, after 10 tons had been applied for 2 
minutes; then 11 tons were applied for 2 minutes; then 12 tons, and 
so, until 15 tons,, or 33,600 pounds pressure, had been tried, when a hook 
of the steelyards broke. Three days afterwards the experiment was 
resumed, beginning with 10 tons, gradually adding ton by ton, until there 
was 31£ tons of upward strain acting upon the pile. This experiment 
lasted 1 hour and 40 minutes, during which time the power upon the 
pile was constant. 

There was afterwards a gradual increase of power to 39 tons without 



21 

moving the pile. It then resisted 40 tons for £ a minute, when it began 
to rise slowly. 41 tons were then applied for If minutes; then 41£ 
tons for half a minute, the pile meanwhile moving upwards at the rate 
of t~2 of an inch per minute. The tests of 40, 41, and 41^ tons, occu- 
pied half an hour, during which, the strain being constant, the pile was 
moved 2-J- inches. 

It was then subjected to a strain of 30 tons for 18 hours, and was not 
moved by it. After which, by adding from 2 to 7 tons, the pile was 
moved, in one hour, three (3) inches; and, after it had moved upwards 
about 6 inches, a power of 25 tons was allowed to remain on it for 2 days 
and did not move it. The pile was then withdrawn from the sand. Its 
extreme length w T as 29 feet. The length of the part which had been in 
sand was 16 feet, including the sharpened end of 2 feet in length; 1 foot 
in depth about this pile was loose sand, which had been once excavated 
and fallen back. The average diameter of the part in the sand was 13| 
inches, including the bark. The bark remained on the entire pile, except 
on 3^- feet of its pointed end. This pile weighed 1,632 pounds. 

A single pile used as a fulcrum for the lever sustained at the most, 
during the experiment, 38-nft- tons weight without settlement. Ex- 
periments showed that piles which one day penetrated ~ro of an inch per 
blow, of a 4,087 pounds hammer, falling 10 feet, was found to penetrate 
J-, ^, and i% of an inch, by 3 similar and successive blows applied the 
following day — the three blows being given in 1 minute. If the pile is 
allowed to remain undisturbed a short time the power to move it after- 
wards is greatly increased. (Stewart's Dry Docks of the United States.) 

McALPINE AND SANDERS' FORMULA FOR BEARING WEIGHT OF PILES. 

The formula deduced by the engineer, Mr. McAlpine, from his labors 
at the Brooklyn navy yard, applicable to rams of l,000ft>s. to 3,000ft>s., 
falling from 20 to 30 feet, was £ = 80 (W -j- .0228 V F— 1.) In which 
£ was the supporting power of a pile driven by the ram "W", falling a 
distance F; £ and W being in tons, and F in feet — and that not more 
than J of the result given by this experience should be borne or relied 
upon for any piles. 

Major Sanders' formula, deduced from his experience in driving piles 
at Fort Delaware, with a ram of 3,500fbs., falling 3^ feet, driving a 

R h d 
pile 4'.2; is 3500 x 42 + 4'.2 = 35000 = 4,375ft>s., the weight which the pile 
8 8 

would bear with safety. (See Stewart's Dry Docks of the United States, 
and Engineer and Scientific Journal, for 1867. 



22 

FOUNDATIONS OF FORT MONTGOMERY ON PILES AND GRILLAGE. 

The foundations of Fort Montgomery, on Lake Champlain, near the 
latitude of 45°, was commenced in 1844, and the driving of 4,383 piles 
was finished in 1846. These piles were capped with a timber grillage 
in 1848. Each pile was calculated to sustain a weight of 7 cubic yards 
of masonry and If yards of earth, or a total weight of 34,125ft>s., or 
15.27 tons. 

The piles were driven about 3 feet apart. The grillage is in two 
courses, the lower one, V 3" wide and 12" thick, is notched down 4" on 
the heads of the piles, and pinned thereto. The upper course at right 
angles to the lower one is 12" square across the piles, and 12" X 8" 
between them, the 12" X 12" being notched 4" down on the lower 
course, thus giving a level floor for the masonry. The length of the 
piles, after being driven and cut off, was from 29 to 33 feet. The fall of 
the hammer at the last blow was from 35' 8" to 36'. The diameter of 
the piles was from 12 to 16 inches at the butt, and 9 J to 14 inches at 
the smaller end. The last penetrations were from 2 J to 6^ inches. These, 
facts apply to 39 piles given as examples and illustrations of the whole. 
The hammer weighed l,630ft>s. The weight of the spruce piles was 
about 39f ft>s. to the cubic foot. The pile weighed was rather more dry 
than the average. At least 401fes. to the cubic foot would be a proper, 
average. 

The compressibility of the soil into which these piles were driven was 
about one-ninth (i) of its entire bulk. 

COLONEL MASON'S FORMULA FOR BEARING WEIGHT OF PILES. 

Colonel Mason deduces the following formula from an investigation 
of the value of this foundation, or the amount of weight with which each 
pile may be loaded: Let h be the height of the fall of the hammer at the 
last blow, s the distance to which the pile penetrates at the last blow, 
l,630ft>s. the weight of the hammer, 960ft>s. the weight of a pile 24 cubic 
feet, and joint weight of pile and hammer 2,590ft>s; g the force of 
gravity (32'J,) or the velocity that gravity will generate in a second 
of time, and V 2 g h = velocity of hammer as it strikes the pile, 
- is yrfi = 115.2, and we have for the value of the retarding force 
1,630 X jiU X H5.2 = 118,175ft>s., or 52.75 tons. Each pile was 
actually loaded with and supported the average weight of 28,575fbs., or 
12.75 tons, besides its own weight (960ft>s.) and that of the grillage, or 
about £ of that which the calculated force of resistance is capable of 
holding in equilibrio. 

In the above case the velocity of the hammer at the moment of impact 



23 

will be V 2 X 36 X 32£ = 48.125 feet per second, and the velocity of 

h g 

the joint mass of hammer and pile will be 48.125 X ilsHf = 30.3 feet per 

yiz i 3Q/ 3 918' 

second = Y', and the retarding force -^j will be -^r^ = 777-5 = 1,468, 

the velocity that the retarding force is capable of destroying in a second 
of time on the joint mass of the pile and hammer is then 1,468 feet. 
But gravity is capable of generating on that mass a velocity of 32£ feet; 
dividing 1,468 by 32J we have 45.63 as the ratio between the retarding 
force and the force of gravity. That is the retarding force is capable 
of holding in equilibrio 45.63 times the joint weight of the pile and 
hammer, or 2,590 pounds X 45.63 = 118,181 pounds. This is within 
six (6) pounds of the previous result. The time (t) in this case 

will be t = y/ = oqti> = qs of a second. 

The same result may be obtained by dividing the velocity destroyed, 
viz., 30'.3, by the velocity the force is capable of destroying in a second 

30 3 2 

of time, viz. 1,468; or ^q — 97 on the supposition of a constant force 
during the short period that it takes to destroy the motion of the pile, 
instead of a retarding force. Colonel Mason concludes his memoir with 
the deduction that Fort Montgomery experience is in favor of a 
coefficient of stability of 3 yq when applied to the calculation under the 
supposition of a constant force, although it in reality, as a general rule, 
decreases by very small decrements towards the terminal penetration ; 
and hence, taking this coefficient as a constant, is erring on the safe side. 
For a more minute detail of Colonel Mason's investigation of this subject 
see papers on Practical Engineering No 5, by Colonel J. L. Mason ? 
Corps of Engineers, U. S. Army, 1850. 

Major Sanders' experiments at Fort Delaware were made with a view 
of deducing a rule for foundation on compressible soils, without any firm 
substratum lying within reach of piles, for calculating what weight each 
pile would bear with safety, by comparing the distance it was sunk at 
the last blow, with the force of the blow, it being understood that the 
pile has been driven to such an extent that for a number of blows the 
penetration has been uniform for equal blows. To ascertain such a rule 
two sets of piles of four each were driven, and a platform built on their 
heads ; they were then loaded with blocks of stone piled regularly on the 
platform ; and at regular intervals of time the amount of subsidence 
caused by the weight, which was periodically augmented, was noticed. 
These piles were not driven through the alluvial; their points were 
about 20 feet from the sandy sub-soil, so that their stability was due to 
the accumulated and constantly increasing resistance of the same medium. 



24 

In one experiment the four piles were driven to a depth of about 24 
feet each, with a pile driver that struck 34 blows in a minute, with a ram 
of 2,000 pounds, and a uniform fall of 6 feet. An artesian well sunk 
on this island in 1834 found mud continuously to a depth of 46 feet 
below low-water mark, then 20 feet of sand, then 30 feet of course sand 
containing shells. It then entered and penetrated for 47 feet a bed of 
marl, which contained boulders. At the penetration of 24 feet, each of 
the blows of the ram drove them about an inch, or exactly yV of the 
fall of the ram. The weight placed on them at first was about 60,700 
pounds, (or about ^ of the product of the friction and the weight of 
the ram.) This weight caused a subsidence in 6 months of 3^" of an inch, 
when 15,000 pounds were added without increasing the subsidence. 
Upon again increasing the weight till it reached 94,000 pounds, (the 
ratio corresponding to which was ^,) the subsidence began again, and in 
a month had attained 3-3- of an inch, when it ceased, or at least made no 
progress during the ensuing three months. The next addition to the 
weight brought it to 107,500 pounds, and the ratio to about -^, and in a 
month increased the subsidence to - 3 - 2 - of an inch. The next addition 
raised the weight to 121,800 pounds, and the ratio to 1:4.6. Tin's weight 
remained upon the piles without alteration till three years and five 
months had elapsed. In the first eight months it had caused the subsi- 
dence to increase from - 3 - 2 - to -g-f of an inch; and this subsidence did not 
increase during the remaining two years and nine months of the period. 
During the ensuing seven months the weight was successively increased 
to 134,000, 147,000, 160,000, 174,000, and finally to 189,500 pounds, 
(or 84.59 tons;) the ratios corresponding to which were respectively 
1:4.19, 1:3.81, 1:3.52, 1:3.23, and 1:2.969. Until the last weight was 
put on no additional subsidence was caused by the increased pressure. 
It will' be seen that the weight, answering to the ratio of 1:4.6 above 
mentioned, remained upheld 3 years and 4 months without the slightest 
variation in the subsidence of the piles, although it was repeatedly added 
to, and the whole system jarred in doing so during that period. But 
upon laying of the last load of stone the subsidence again began, and at 
the end of the ensuing period of 1 year and 5 months had arrived at 
if of an inch. This subsidence did not go on uniformily, but by steps 
at a time. It seemed to be ceasing at the end of the period, judging 
from the facts that the intervals of rest were longer and the successive 
subsidence less towards that date, viz: April 12, 1856. The next time 
that the observations were made on the levels of the pile heads was on 
the 24th of April, 1860. The subsidence had then arrived at an average 
of 1 inch within an appreciable fraction, showing an increase in 5 years 
and 5 months of - 3 - 2 - of an inch. It is probable that this subsidence took 



25 

place within the 2 or 3 years that followed the date of April 12, 1856, 
and that the piles have remained immovable for the last 2 years at least. 

The whole period over which this experiment extended was (May, 
I860,) about 9£ years. The conclusions that may be derived from it are 
obvious; that the subsidence had ceased may be safely assumed. It 
follows that a building on piles, driven in soils exactly of the nature 
of that in which these experimental piles were placed, will be safe if 
we do not load them with a greater weight than the third part of the 
quotient arising from dividing the product of the weight of the ram 
and the distance it falls, by the distance the pile is sunk by the last 
bloiv. The coefficient was, however, fixed by Major Sanders for safety 
at J. Conversely, having given the weight of the superstructure, we 
can by the same rule ascertain the minimum number of piles that will 
sustain it if driven to a fixed depth, or the depth to which an approx- 
imately fixed number of piles must be driven to effect the same purpose. 

There were two experiments of the kind we have described made at 
Fort Delaware. The second one continued 3 J years, had similar results, 
and was equally regarded in the determination of the coefficient used in 
the rule. 

From other experiments made during the same period, Major Sanders 
ascertained the relation between the living force of the ram and the 
distance the pile is sunk for different falls by a series of experiments on 
64 piles, which received 1,900 blows from a ram of 800 pounds. It was 
found that when the fall was less than 3 feet, the useful effect was extremely 
small ; that it gained in a rapidly increasing ratio as the fall was aug- 
mented, a foot at the time, to 5 feet; and that at this point the ratio of 
useful effect to the force expended is at its maximum, and that the piles 
are driven to distances proportional to the blow; or, in other words, that 
there is nothing gained by increasing the fall beyond 5 feet — for example, 
2 blows of 5 feet will sink a pile as much as 1 blow of 10 feet; 3 blows 
as much as 1 of 15 feet; 4 blows of 5 feet as much as 1 of 20 feet. It 
was also found that if the 5-foot blows followed each other in rapid suc- 
cession the useful effect was rather greater than if the interval employed 
in common hand-power machines for hoisting the ram was allowed to 
elapse. 

From 1833 to 1838 eleven thousand (11,000) piles, of 45 feet in 
length, 12 inches square at the head, and not less than 10 inches diameter 
at the small end, were driven for the foundations of Fort Delaware, 
under the superintendence of Captain Delafield, of the Corps of Engi- 
neers, with a hammer of 1,800 pounds, by blows in quick succession, 
with steam power — the maximum fall of the hammer being 45 feet. 
Since 1850, four thousand five hundred (4,500) additional piles were 



26 

driven under Major Sanders' superintendence, from which experience he 
has drawn the preceding deductions. Six thousand six hundred of these 
piles are under the scarps and casemates of the present work. (See Lieut. 
Morton's Life and Services of Major John Sanders, of the Corps of 
Engineers, 1861.) 

In 1848 the excavations for the foundations of the work existing at 
this time (1868) were commenced and completed in 1849, and the piling 
by Major Sanders, heretofore referred to, was finished in 1851. By 
1853 two thousand tons of masonry had been laid on these piled founda- 
tions, and in 1859 the walls, arches, and other masonry were finished. 

Three bench marks were established in 1854, reference to which was 
made in 1859, when it was found the masonry had not settled in any 
part. 

From 1859 to October, 1866, the settlement on reference to the above 
bench marks was 4" at the maximum point, and 2". 65 at the minimum, 
and a mean settlement for all the observed points of 3".19. No crack was 
perceptible in any part of the work in 1866 or in 1868. (See Keports 
of Superintendent at Fort Delaware.) 

KESISTANCE OF PILES DRIVEN AT THE S. W. PASS OF THE MISSISSIPPI 
RIVER, ON STAKE ISLAND. 

Stake Island consists of two mud lumps, forming its northwest and 
southeast extremities, about 500 yards apart. At both points the ground 
is high, of the character of other mud lumps. 

The space between the two mud lumps is much lower, presenting the 
same general features and vegetation as the land on either side of the 
river. The ground between these two lumps is about as solid as anywhere 
higher up on the river between the passes and the city. The experimental 
pile driving commenced on the 19th November, 1867. 

Pile No. 1 was 30 feet long. After 12 blows the head of the pile 
within 1' 6" of the ground, was rent to pieces. The head of the pile was 
square timber, 11 inches at the upper end, and 10 inches diameter at the 
lower end, banded with £-inch iron 3 \ inches wide. Outside diameter 
%\ inches. The broken part of the pile was then cut off, and a piece 
15 feet long set on top of it. 17 more blows were then given when the 
pile gave way, tearing the head completely off. The total depth obtained 
by these 29 blows was 41' 11", being driven to low water mark, and 
level with the lowest soil. 

Pile No. 2, after 12 blows, was broken at the head, cut off, and a 
piece of 17 feet in length set upon it. 23 additional blows drove the 
pile down to 45' 1" below the surface of the ground. 

Pile No. 3, 30 feet long. After 11 blows the head of the pile was 



a 


% 


a 


3, 


a 


4, 


No. 


1, 


a 


2, 


a 


3, 


a 


4, 



27 

badly rent 4' 6" above ground. 3' 9" were cut off, and a piece of 
18' 6" set on, when with 9 blows the head gave way. 5' 1" was then 
cut off, and with 7 more blows the pile was 35' 8" below the surface. 

Pile Wo. 4 was the same size as the previous piles. After 10 blows the 
head was 1' 8" above ground, and was then cut off, and 16 feet set on; 
27 more blows were given, and V 9" cut off; when a piece of 16 feet 
was set on, and after 13 more blows 4 feet were cut off, leaving the pile 
54' 2" in the ground, and 5 inches above. 

The maximum fall of the hammer was 28 feet. The size of the 
hammer, of cast iron, was about 2' 5" high, V 8" wide, and V 1" thick. 
The penetration of these piles was as follows : 
No. 1, with the first blow falling 5' 9", was 6' 3". 
« " « " V 6", " r 8". 

" " « 4' 3", " 9' 1", 

" " " 3' 6", " 11' 4". 

with the Zastf blow falling 28' 5", was 10 inches. 
" " " 28' 7", " 11 inches. 

" " " 26' 6", " 9 inches. 

" " " 25' 5", " 14 inches. 

See Bonzano to Gen. McAlester, 9th January, 1868. 
In March, April, and May, 1868, 45 piles, of 50 to 60 feet in length, 
were driven under the direction of General McAlester, at St. Joseph's 
Island, in the same alluvial soil as deposited from the Mississippi river. 
The same remarkable uniformity of penetration, by the successive blows, 
was developed as at Stake Island. See McAlester's report of 5th 
May, 1868. 

GRILLAGE FOUNDATIONS. 

A third system of foundations for compressible soils is that of the 
grillage, resting on the natural formation on the surface or at any 
selected depth. 

The following are examples of this character by engineers who have 
constructed many edifices on this principle in the United States : 

The earliest structure of this character, of which the writer has infor- 
mation, is a building at the Balize Bayou of the Mississippi river, near 
the site of the pilot houses. It is of brick masonry, constructed by the 
Spaniards or French during the early settlement of the country, and 
apparently for a magazine. It had settled so deep, up to the year 1829, 
as to make it impracticable, at that time, to ascertain the uses to which 
it may have been applied. From the practice of the inhabitants of the 
country it is inferred, in the absence of positive knowledge, that a grillage 
was used in this case. 



28 

In 1807 a survey of the coast of the Mississippi had been made and 
the outlets of the Mississippi particularly examined to select the most 
eligible site, best material, and plan for a light-house. A commission, 
appointed by the President of the United States, in 1816, again explored 
the various mouths of the river and the different islands situated there, 
and concluded that the most proper situation was at the mouth of the 
Northeast Pass of the Mississippi river, on Frank's Island. They 
say " this site appears to have undergone all the changes experienced by 
the different Islands here in the course of their formation and consolida- 
tion, being elevated about 3 feet above the surface of the river, and the 
only island not covered with water during the last hurricane." They 
bored the island and found the soil, for 35 feet, a mixture of clay and 
fine sand, and to the depth of 50 feet, a dark blue clay without any 
mixture of sand or vegetable matter. This clay grew harder as the borings 
descended. This commission designed a plan for this locality, the structure 
to be built of stone and brick, recommending that for a foundation, the 
surface to be covered by a light-house, be dug down to the level of low 
water, and this space be filled with piles 25 feet long, one foot diameter, 
driven as close as possible, and as long as they can be forced down with 
the " battering ram" then cut off at the surface of the water, laying 
upon their heads one foot square timber of the greatest length that could 
possibly be procured, and not more than 1' 6" apart, crossing these with 
another layer of the same dimensions, filling the intervals between the 
timbers with shells, or rubbish beaten down and united by pouring in 
grout; covering this with a close floor of 4-inch plank, spiked to the 
timbers. Upon the floor the foundations may be laid, taking the pre- 
caution to turn reversed arches under all the walls. The weight to be 
diminished comparatively by making it bear on the greatest surface 
possible. (See State papers on commerce and agriculture.) 

A light-house of stone and brick masonry was afterwards built at this 
locality. After being finished it soon settled irregularly, and finally 
inclined to one side so much as to make it necessary to take down the 
whole structure, before the year 1824. Soon after which period the 
material was in part transported to and used in the construction of Fort 
Jackson, about thirty miles up the river. By reference to the original 
drawings of Mr. Latrobe, (who constructed the building,) and loaned me 
by his brother, Benj. H. Latrobe, of Baltimore, it appears that the 
masonry of this tower was 81 J feet high, and 19 feet diameter at the 
base, resting on 53 piles of ten feet in length. 

The foundations of Fort Pike, on the Rigolets, were commenced about 
the year 1820. The soil is very similar to that at the mouths of the 
Mississippi, the surface being mostly vegetable matter underlaid by a 



29 

combination of vegetable earths and dark clay. The foundations of the 
scarps and piers of the casemates were all laid on a grillage of round 
pine logs, side by side, resting on the excavated soil, and crossed on top 
at right angles, by similar logs, of from 10 to 12 inches diameter, 
and about two feet apart in the clear. The masonry of the piers was 
built in and thus united to the masonry of the scarps. The work was 
finished about the year 1828. The foundations are about six feet below 
the level of the waters of Lake Pontchartrain, and the ground below that 
level is saturated with water. 

The work settled irregularly. The masonry of the casemate piers 
broke from the scarps, making cracks about 4 inches wide. The timber 
grillage in this case failed to overcome the compressibility of the sub-soil, 
or to preserve uniformity of settlement. (Personal recollection.) 

Fort Wood, on the Chef Menteur Pass, (La.,) (now, 1868, Fort 
Macomb,) was commenced about the year 1825 and finished in 1832. 
It is situated at the end of a dry clay ridge following the bank of the 
Metairie Bayou, from near New Orleans, to the entrance of this bayou 
into Pass Chef Menteur, and is the firmest soil on which any of the forts 
in Louisiana are constructed, the natural surface being 3 feet above the 
waters of the Pass and Lakes Pontchartrain and Borgne. This dry ridge 
is wooded with heavy live-oak timber. The foundations of the scarps 
and casemates are similar to those of the fort on the Rigolets, and the 
general plan of the work similar. It was finished about the year 1832. 
The foundations were about six feet below water, and the ground saturated 
from the lake level to the depth of the excavations. The excavations 
were in a firm adhesive clay soil ; hand pumps and buckets sufficed to 
keep down the water during the excavations. 

In this case there was no such irregularity of subsidence as to injure 
the work, although extensive repairs were necessary in consequence of 
this irregularity. The grillage did not suffice to overcome the compres- 
sibility of the subsoil, or preserve uniformity in the levels of the masonry. 
(Personal recollection.) 

The foundations of Fort Jackson, Placquemine bend of the Mississippi 
river, were commenced in 1825; the masonry was finished and ramparts 
formed, ready to receive the parapets, in 1832, at which time the work 
was suspended to give time for settlement. The subsoil in this case is 
very compressible and saturated with water at all times from near the 
surface to and below the bottom of the foundations, about 11 feet below 
the natural level of the country. Vegetable matter composed the upper 
layers, under which, it is combined with dark clay. The problem in this 
case was to create uniformity of pressure and settlement by underlaying 
the masonry with a strong grillage of timber laid on a plank floor. The 



30 

plank was laid on the excavated earth and large cypress timber, 12 inches 
thick, 15 to 24 inches wide, laid longitudinally upon it, edge and edge, 
formed a solid continuous floor. On the top of this solid flooring, other 
timbers, 12 inches thick, and from 15 to 18 inches wide, were laid 3 feet 
from centres, perpendicular to the lower courses. The spaces between 
these last timbers were filled, solid, with brick masonry laid in cement 
mortar. This grillage projected three feet in front and rear of the fair 
masonry of the scarps, which were from 8 to 10 feet thick. The grillage 
and foundations of the casemates were constructed in like manner. The 
result, seven years after the commencement of the foundations, was une- 
qual settlement of various parts of the work, and cracks in the masonry 
of the scarps on the faces and flanks of the bastions. It became neces- 
sary to lighten the load of embankment pressing on the foundations. 
The earth pressing against the centre of the scarps of the bastion faces 
and of the solid curtains, was removed to the depth of the grillage of the 
casemates, and hollow vertical brick cylinders, of 18 feet diameter, cov- 
ered with hemispheres of brick masonry, were constructed behind the 
faces of the bastions, and three horizontal bomb-proof store rooms were 
built on the centres of the solid curtains. 

No stronger or more substantial grillage is known to have been con- 
structed in Louisiana. In 184:2 the casemates of the two water fronts 
and gate- way fronts were a second time loaded with an excess of weight 
to restore the levels and guard against future inequality of settlement. 
In 1851 the floors of the casemates of the flanks had to be raised and 
other repairs made, in consequence of unequal settlement. 

The grillage failed to preserve uniformity of settlement, and the com- 
pression of the subsoil was not overcome by this application of a timber 
platform distributing the weight over a great surface. (Personal knowledge. ) 

Battery JBienvenue, on the bayou of this name, emptying into lake 
Borgne, was commenced about the year 1828. It is founded upon a 
grillage of round pine logs, averaging 12 inches diameter, laid on a plank 
floor, and overlaid by 12-inch pine logs, at right angles to the lower layer, 
and distant about 3 feet from centres. This grillage is founded four feet 
below the surface of the water of the bayou. The soil is but little better 
than a prairie tremblante. Borings were made 20 feet deep, indicating 
vegetable soil only, combined with a large percentage of water. The 
grillage is arranged precisely similar to those of Chef Menteur and the 
Rigolets. The masonry consists of a low scarp, backed by an earthen 
rampart. The masonry settled several feet before the scarp was finished, 
with great irregularities ; the centre of each line of the trace of the work 
settling some feet below the ends. A square magazine, built on an inde- 
pendent grillage, similar to that under the scarps, settled, soon after the 



31 

bomb-proof arch was turned, several feet, bringing the lintle of the door- 
way down to the surface of the ground. In this case the grillage failed 
to either secure a uniformity of settlement or overcome the compressibility 
even to such an extent as to fulfill the desired useful purpose. Great 
and extensive repairs and additions have been since made to this work. 
( Personal recollection.) 

Southwest Pass .Lighthouse was built in 1831. It is about 65 feet 
high, and built of wood. It rests on a timber grillage, of unknown 
dimensions. It has failed to secure the conditions necessary for a founda- 
tion and has now to be rebuilt, having inclined so far from the vertical 
as to render a hastened reconstruction desirable. The site of this light- 
house is on one of the upheaved islands common to the mouth of this 
river. (Records of the Light-house Board.) 

The St. Charles Hotel, in the city of New Orleans, was commenced 
in 1836 and finished in 1837. It was destroyed by fire in 1851. The 
foundations were of brick masonry, on a grillage of heavy flat-boat gun- 
wales of 60 to 80 feet in length, 20 to 30 inches wide, and 6 to 12 inches 
thick, and laid about 6 feet below the sidewalk. This building settled 
2 feet in 12 or 14 years. The present hotel (1868) was commenced in 
1851, on top of the old foundations, and finished in 1853. It has settled 
fully 12 inches more (in addition to the settlement of the former building) 
in the last 15 years, making a total compressibility of the subsoil of 3 feet 
since 1837, or in 31 years. In this case a grillage has failed to secure 
the desired object. (Henry Howard to Gen. Delafield, June, 1868.) 

The Light-house at Pass d V Outre was built in 1855. It is a cast-iron 
shell, about 65 feet high, resting upon a masonry base 4' 6" thick, extend- 
ing a like distance (4' 6" ) beyond the base of the tower and under the 
whole structure. In 1864 an interior brick lining was added. It is 
not known that any timber underlays the masonry. This masonry, how- 
ever, covering the entire surface occupied by the building, with 4' 6" 
offsetts beyond it, fulfills all the conditions of underlaying timbers. The 
site on which it is built is firm on the surface and is about 3 feet above 
the level of the gulf of Mexico. It must, therefore, be upon one of the 
upheaved islands common at the outlets of the Mississippi. It has settled 
unequally, one side leaning from 9 to 12 inches in its height. 

In this case the grillage or masonry base has failed to secure either 
uniformity of settlement or to overcome the compressibility. The keeper's 
house at this locality is a 1^-story wooden structure, resting on 9 brick 
piers of 18 inches square each, under which is a grillage 6 feet square, of 
two thicknesses of round logs. It has settled 2^- feet and now requires 
repairs (1868) to correct the consequent defects. The grillage has, in 



32 

this case, failed to secure the desired stability. ( Bonzano's report to the 
Light-house Board, Washington.) 

The First Presbyterian Church, in New Orleans, was commenced in 
1846 and finished in 1857. The main tower is 20 feet square and 115 feet 
high, surmounted with a wooden spire. The foundations were built of 
brick masonry, laid in cement mortar, on a grillage of two thicknesses of 
flat-boat gunwales of 45 feet in length, crossing one another. The 
excavation was 12 feet below the surface of the street. The bottom was 
a hard, stiff, blue clay, the best my informant has ever seen, after thirty 
years' practice as an architect in New Orleans. It has settled 5£ inches 
in 11 years. (Henry Howard to Gren Delafield, June, 1868.) 

Fort Calhoun, now Fort Wool, Hampton roads, Ya., was commenced 
in April, 1819, when the first stone was deposited on the Kip-rap shoal 
for its foundation, in 21 feet water. The shoal and adjacent shores of 
the Chesapeake bay and Hampton roads are hard sand. It was deter- 
mined to construct the superstructure of a four-tier casemated masonry 
battery at this locality, on an enrockment of quarry stone, thus forming 
an island similar to the Plymouth and Cherbourg breakwaters. During 
the first year's labor the enrockment was brought to the surface of the 
water on the line of the southern face of the work, and in 1821 the sur- 
face had been enlarged to receive the entire foundations of the super- 
structure, for which preparations were made and commenced in 1826. 
The enrockment was added to, and an area of several acres was formed, 
terminating with a long slope, to intersect the shoal; equivalent to a 
grillage for the proposed superstructure, spreading the pressure of the 
walls at least 25 feet beyond their exterior lines. The foundations of the 
casemates on the water fronts were all laid, and the scarps and piers of 
the casemates raised to the springing lines of the arches of the embrasures, 
when numerous cracks in the masonry and irregular settlement of the 
work throughout its whole extent indicated that the foundations could 
not be relied upon. It was determined to suspend the construction of 
the work in 1829 or 1830, and load the foundations of the scarps and 
casemates with a weight greater than that of the castle in its finished state, 
with its armament, stores, and garrison. 

In 1833, eleven thousand (11,000) tons of building stone were piled 
over and near the walls, bearing on their foundations. 

In 1831, sixty-one thousand eight hundred and sixty-six tons (61,866) 
were added. The annual subsidence with this increased weight at the 
centre of the work was ^ less than it was in 1833, and those parts that 
formerly settled most, now settled least. 

In 1835, twenty thousand tons more than the estimated required 
quantity was resting upon and along the whole extent of the foundations. 



This accession of weight continued to cause subsidence, though in a 
decreasing ratio. 

In July 1836, the stone for the superstructure and materials accumulated 
for compressing the foundations were being removed upon the supposition 
that the base on which the castle was to rest had been satisfactorily 
compressed. In 1837 the load of stone was entirely removed from the 
foundations, continued subsidence was however observed, and the founda- 
tions were immediately reloaded. 

In 18-10, a total weight of 55,716 tons had been reloaded on the 
foundations, increased subsidence was still observed. In November 1842 
there was an excess of 13,627 tons on the foundations, beyond the ultimate 
weight to be supported. The average subsidence in 1841 was ^ of an 
inch; compared with former years it was in a decreasing ratio. In 1843 
it was found that the mass was still settling, when an additional load was 
recommended. In 1846 the subsidence was f of an inch, and up to 1850 
the diminution of settlement was progressive. 

The total average subsidence of the foundations from 1830 to 1856, 
accurately noted from year to year, w T as at the greatest point 5.28 feet, 
and at the least 4.35 feet. It was immovable from 1850 to 1856. From 
1841 to 1847 the maximum average settlement was xo~o °f a foot. The 
total subsidence of a tide pier from 1824 to 1851 was 6.63 feet. (See 
Annual Keports of Chief Engineers, accompanying President's Message.) 

Custom-house^ JVevj Orleans, (La.) This building w r as commenced 
in 1848, and progressed from time to time until 1860. It is founded 
upon a flooring of plank laid on the excavation seven feet below the 
street pavement. On this floor a timber grillage is laid of 12 inch logs, 
" side and side," over which similar logs are placed transversely, distant 
from each other 2 to 3 feet in the clear. 

The space between the timbers is filled with concrete, which is con- 
tinued over the whole grillage for a depth of one foot. Counter arches 
of 1-J- bricks thick support the walls of the interior subdivisions of the 
building, thus throwing the weight of the building upon the entire 
surface included within the outline of the building. 

As a concrete and grillage foundation to support this heavy building, 
no greater surface, to resist the weight and pressure of the walls, could 
well be attained. , 

The walls, of 2' 6" thick, rest on grillage timbers 10 ft. wide. 

Those of 4' " " " * 15 ft. " 

And those of 9' " " " 20 ft. " (abutments.) 

In 1860 the granite walls of this building had been carried up 75 feet 
above the concrete base to the architrave line of the entablature, and all 
the iron floor beams of the fourth story finished. 

Memoir, etc. 3 



34 

The exterior walls are four feet thick, exclusive of projections ; 2-J- feet 
of which is brick masonry, and 1 J feet of stone masonry. 

In 1851 a commission reported that borings at the custom-house, and 
at a point not far removed from it, indicated different degrees of com. 
possibility. It is situated upon the firmest, dryest, and most reliable 
ground in and about the city of New Orleans. 

The maximum settlement of the building in any one point, up to 1860, 
was 2' 6". This compressibility of the soil beneath the grillage was very 
variable. 

From 1848 to 1851 the maximum settlement was 22.57 inches, and 
the minimum in the same time was 15.63, making a difference of level 
in various parts of the building of 6.94 inches. 

In the year 1857-58, the maximum settlement was 3.50 inches, and 
the minimum 0.66, making a difference of settlement this year of 2.84 
inches ; and in 1858-59, the maximum was 2.63 inches, and in many 
places nothing, making a difference of settlement, level and compressi- 
bility, this year of 2.63 inches. 

The line of the exterior walls in 1864, on which the temporary roof 
rests, varies in the level 3 inches. 

This grillage covers a surface of about 300 feet square, and although 
well constructed, and with great care, it has failed in its objects. (See 
Records of the Treasury Department, Bureau of the Architect.) 

Fort Sumter, Harbor of Charleston, was constructed upon an enroek- 
ment similar to Fort Calhoun, now Fort "Wool. In 1840 the settlement 
was such as to induce the superintending engineer to recommend that it 
be loaded with a weight equal to the maximum, with its armament and 
munitions that could rest upon its foundations. In 1850, the engineers 
reported the subsidence of this work to be continuous, though in a 
decreasing ratio annually. At this time the scarps and two tiers of case- 
mate arches were completed. 

CONCLUSION. 

The plan proposed by a committee of the Light-house Board, in 1868, 
is again referred to the same committee, increased by two other members 
of the board to consider the whole subject anew. The plan then approved 
by the board is appended hereto ; which, with the practice and views of 
many experienced engineers in compressible soils, is presented, with the 
belief that the best plan suited to this most difficult locality, may be more 
satisfactorily devised with the information now embodied in this memoir 
for the consideration of the committee. 

Extracts-. "Considering the impracticability of finding any solid 
natural base at the outlets of the Mississippi, or any locality calculated 



to sustain tlis weight of an iron light-house, without extraordinary aids 
from art; and the extraordinary geological formation of the country 
about the Passes of the Mississippi, all going to show that great and 
unusual precautions are necessary to secure a foundation for any weighty 
structure at or about the outlets of the Mississippi, the committee proposes 
some modifications of the plans submitted to it, with the hope of securing 
greater solidity, and to a greater depth of the natural soil to resist the 
settling of an iron light-house for the proposed locality at the Southwest 
Pass." 

"The first precaution is that the superstructure to rest on this founda- 
tion shall be of the least practicable weight to fulfill all the conditions for a 
permanent light-house, and then that the soil of the selected site be 
solidified to the greatest practicable depth by wedging it with wooden 
(pine) piles of about 50 feet in length, not less than 12 inches square at 
the head, and not less than 10 inches diameter at the lower end, driven 
into the soil with a hammer t)f not less than 1,800 lbs. weight, with a final 
tall of 45 feet, continuing the operation of driving until the head of the 
pile may pass below the ways of the pile engine, and thence by a punch 
to the surface of the soil, or until the head of the pile, battered into fibres, 
no longer transmits the percussive action ot' the ram to the solid wood of 
the pile. These piles should be driven in rows, 3' 6" from centres, 
throughout the entire surface of the site to be occupied. After driving 
this series of piles a judgment can be formed of the practicability of giving 
additional solidity to the natural soil by driving another series of piles of 
the same dimensions (or somewhat smaller diameter) at the intersection of 
the diagonal lines drawn from the heads of four consecutive piles of the 
first series, and 3' 6" from their own centres in their own parallel lines 
or roads." 

" ~No more timber than of these two series can probably be driven into 
the soil. Should the contrary be the case, the site should be abandoned 
as approaching too near a semi-fluid to justify the construction of any 
permanent structure thereon." 

"Having thus solidified the soil by wedging with timber, the heads of 
all the piles of the first series are to be cut off level, to a uniform depth 
of 2' 6" below the lowest low water, and the heads of the second series 
to a uniform level of V 6" below the lowest low water." 

"The next operation will be to secure the heads of all those piles in a 
fixed position in relation to each other, and from being inclined by the 
superincumbent weight of the light-house. This will be effected by 
excavating the soil to a depth of 1' 6" below the heads of the first series 
of piles cut to a uniform level as above required; (it may be found more 



36 

advantageous to make this excavation before driving any piles, to admit 
of floating the pile engine on a scow, a great economy where practicable ;) 
or, to a depth of 4 feet below the lowest low water. 1 ' 

"The space below and between the heads of the first series of piles to 
the depth of V 6" will then be filled with concrete to the heads, care 
being taken to pump out all the water, that the concrete can be rammed 
thoroughly between the piles and into the soil on which it is first deposited. 
This concrete will be brought to the level of the heads of this series of 
piles, thus bracing them from each other by a hard, durable, and continuous 
mass of concrete of 1/ 6" thick over the whole surface of the foundation." 

" Over the heads of this first series of piles, and resting also upon the 
concrete surface between them, horizontal timbers (cypress or pine) will 
be laid, 12 inches thick, by 15 to 18 inches wide, when another layer of 
concrete will be rammed about these string pieces and the heads of the 
second series of piles; then a row of horizontal 12-inch timbers at right 
angles with the first, of 15 to 18 inches wide, will be laid over the heads 
of the second series of piles, and concrete filled in solid to the surface of 
the second layer of horizontal bearing pieces. The string pieces resting 
on the heads of the piles may be toenailed thereto to keep them in place 
while the work is being constructed." 

"We have now solidified the soil to a depth of 50 feet, and above it 
formed a solid floor of timber and concrete, resting upon and covering 
the entire base thus solidified by wedging." 

"Upon this last surface, which is 6 inches below the lowest low water? 
completely excluded from the air, the foundation of the masonry for the 
support of the iron of the superstructure will be commenced." 

The foundation of the base of the iron work should be four feet 
above ordinary high water. "This foundation, down to the level of the 
timber grillage, should be formed of solid brick or stone masonry, spread- 
ing out to cover the greatest possible surface, by offsetts in every course 
of brick or stone of which this part may be constructed. Between this 
exterior base and the centre, the entire foundation will be raised with 
concrete to the natural level of the shoal. As these parts cannot have 
any weight of the superstructure (of the proposed design) upon them, 
any superfluous mass of material but adds to the risk of settling." 

"The superstructure should be designed to throw the weight not only 
on the corner posts, but upon the spaces from one of these corners to the 
other, and also upon the radii connecting these corners with the centre 
column. With this in view the masonry on these lines, from the timber 
platform, should be built with offsetts to cover as much surface as practi- 
cable. The bed-plate of the superstructure resting on the masonry should 
be bolted with composition bolts, securing them to the under part of the 



37 

concrete and timber platform, to give some additional stability to the base 
against the action of the wind.' 1 

" Notwithstanding all these precautions, it is considered advisable, pre- 
viously to raising the superstructure, to load the entire surface of this 
artificial foundation with a weight of matter greater than the entire load 
it can ever be required to sustain. This load should remain at least one 
year, when an examination should be made as to the propriety of com- 
mencing the superstructure, suspending the work, adding to the load and 
await another year, or abandon the site altogether." 

The weight of cast and wTOught-iron of the superstructure of the plan 
submitted to the committee is 400,000 lbs. This may be greatly reduced by 
the adoption of modification of the design of the framing of the wrought- 
iron work. Reference to the Practice of European Engineers for such 
structures may be found in Proceedings of the Institution of Mechanical 
Engineers for 1861, giving a detailed description of the light-house at 
Buda, Spain. Minutes of Proceedings of the Institution of Civil Engi- 
neers, vol. 23, for a description of the Ushruffee light-house, in the Red 
sea, and the Engineers' and Architects' Journal for Jan. 7, 1868, for 
description of the light-house for the Douvres. 

RICH'D DELAFIELD, 

Brevet Major General, 
Corps of Engineers, U. S. Army. 



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